Not totally sure what cities/types of events you were considering having here, but I looked for some west coast cities/events that struck me as possible places for someone to stir up trouble.
SF was really the only useful website for the four cities I tried. But here are the links to the sites at least...
San Francisco http://www.sfvisitor.org/visitorinfo/html/memorial_day_events.asp
May 31
Lost Boat Ceremony
A contingent of World War II submarine veterans and their families will participate in a Memorial Day tribute to World War II submariners on "eternal patrol" at 11am. The formal and touching remembrance will conclude with the Lost Boat Ceremony, during which the USS Pampanito's bell is rung and wives and widows of veterans drop 52 carnations into the Bay - one for each of the submarines lost during World War II.
July 4
Any of a number of 4th of July events
LA
http://www.ci.la.ca.us/
not finding much for LA...website for the city isn't great as far as events in my searching
San Diego
http://www.sannet.gov
The events calendar only is helpful for a week out unless you go day by day searching...
Seattle
http://www2.ci.seattle.wa.us/events/default.asp
Victoria Hen, RIP
http://news.bbc.co.uk/1/hi/world/americas/2115560.stm
More...
And I think all major cities having big Memorial Day or July 4th Celebrations are probably automatically events you are thinking of as potential targets, right?
New York
www.nycvisit.com/calendar
Fleet Week
Intrepid Sea-Air-Space Museum | West 46th Street @ 12th Avenue | A huge celebration with ships from around the world, troops, and military aircraft.
June 19th
Athens 2004 Olympic Global Torch Relay
Athens 2004 Olympic Organizing Committee | Citywide | The first-ever global journey of the Olympic Torch will span 34 cities and 26 countries over 35 days. New York City will celebrate the arrival of the Olympic Torch with an approximate 35 mile run through the streets of the City, followed by a public celebration honoring the Olympic Spirit and the Athens 2004 Games.
Didn't think of the torch till I saw this and was reminded...so that should also go for any other torch city, perhaps...including LA, St. Louis, and Atlanta (in the US) http://www.athens2004.com/athens2004/page/legacy?lang=en&cid=9f587ae4be659f00VgnVCMServer28130b0aRCRD
Boston
www.cityofboston.gov/calendar
Title: Boston Seaport Festival
Celebration of the summer season around Boston Harbor featuring a variety of activities for families to enjoy.
Start Date: 6/12/2004
End Date: 6/13/2004
Title: USS Constitution Cruise (AMONG OTHERS ON JULY 4)
The world's oldest commissioned warship afloat and symbol of American spirit, will get underway in salute of the nation for its outstanding support of our armed forces during her traditional Fourth of July Turnaround Cruise. The ship will travel approximately three miles into Bosotn Harbor to the Castle Island area.
Location: USS Old Ironsides
Pier One
Historic Charlestown Navy Yard
I added your list to the TM back-up site.
Thanks! V, would you please post this on our backup TM?